1. Field of the Invention
The present invention relates to a piezoelectric ink-jet printhead. More particularly, the present invention relates to a piezoelectric ink-jet printhead including a nozzle plate integrally formed with a heater for heating ink and a method of manufacturing the nozzle plate.
2. Description of the Related Art
Generally, an ink-jet printhead is a device that ejects small volume ink droplets at desired positions on a recording medium, thereby printing a desired color image. Ink-jet printheads are generally categorized into two types depending on which ink ejection mechanism is used. A first type is a thermal ink-jet printhead, in which ink is heated to form ink bubbles and the expansive force of the bubbles causes ink droplets to be ejected. A second type is a piezoelectric ink-jet printhead, in which a piezoelectric crystal is deformed to exert pressure on ink causing ink droplets to be ejected.
FIG. 1A illustrates a plan view of a conventional piezoelectric ink-jet printhead. FIG. 1B illustrates a vertical cross-sectional view taken along line I-I′ of FIG. 1A.
Referring to FIGS. 1A and 1B, a flow path plate 10 having ink flow paths including a manifold 13, a plurality of restrictors 12, and a plurality of pressure chambers 11 is formed. A nozzle plate 20 having a plurality of nozzles 22 at positions corresponding to the respective pressure chambers 11 is formed on a lower surface of the flow path plate 10. A piezoelectric actuator 40 is disposed on an upper surface of the flow path plate 10. The manifold 13 is a common passage through which ink from an ink reservoir (not shown) is introduced into each of the plurality of pressure chambers 11. Each of the plurality of restrictors 12 is an individual passage through which ink from the manifold 13 is introduced into a respective pressure chamber 11. Each of the plurality of pressure chambers 11 is filled with ink to be ejected and collectively they may be disposed at one or both sides of the manifold 13. Volumes of each of the plurality of pressure chambers 11 change according to the driving of the piezoelectric actuator 40, thereby generating a change of pressure to perform ink ejection or introduction. To generate this change in pressure, an upper wall of each pressure chamber 11 of the flow path plate 10 serves as a vibrating plate 14 that can be deformed by the piezoelectric actuator 40.
The piezoelectric actuator 40 includes a lower electrode 41, piezoelectric layers 42, and upper electrodes 43, which are sequentially stacked on the flow path plate 10. A silicon oxide layer 31 is formed as an insulating film between the lower electrode 41 and the flow path plate 10. The lower electrode 41 is formed on the entire surface of the silicon oxide layer 31 and serves as a common electrode. The piezoelectric layers 42 are formed on the lower electrode 41 and are positioned on an upper surface of each of the pressure chambers 11. The upper electrodes 43 are formed on the piezoelectric layers 42 and serve as driving electrodes for applying a voltage to the piezoelectric layers 42.
To apply a driving voltage to the piezoelectric actuator 40 having the above-described structure, a flexible printed circuit (FPC) 50 for voltage application is connected to the upper electrodes 43. More specifically, driving signal lines 51 of the flexible printed circuit 50 are disposed on the upper electrodes 43 and then are heated and pressurized to bond the driving signal lines 51 to upper surfaces of the upper electrodes 43.
However, when the above-described conventional ink-jet printhead is used to eject high viscosity ink, flow resistance increases due to the high ink viscosity, thereby decreasing the ejection volume and ejection speed of ink droplets. Therefore, overall ink ejection performance is lowered, which renders printing quality unsatisfactory. In this respect, to ensure satisfactory ejection performance for high viscosity ink, reduction of ink viscosity by heating the ink with a heater is required.
For example, one conventional ink-jet printhead includes an ink cartridge in which a heater for heating ink is mounted outside the ink-jet printhead. In this conventional ink cartridge, however, since the heater is located relatively far from a nozzle plate, a temperature profile relative to the location on the nozzle plate heated by the heater is not uniform. Therefore, ink temperatures of nozzles arranged in the nozzle plate is also non-uniform, thereby causing a variation of the ejection speed and volume of ink droplets through the nozzles. Furthermore, the heater separately mounted outside the ink-jet printhead increases the complexity and size of the ink cartridge.
When ink is heated using a heater as described above, ink temperature detection for controlling an ink temperature is required. One such conventional method includes a technique of controlling printing quality by detecting an ambient temperature using a thermistor and estimating physical properties of ink from the detection result. However, this technique has a disadvantage in that an ink temperature value estimated from a detected ambient temperature may vary depending on operating conditions of a printhead.